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In our view, the four principles for making evidence synthesis more useful for policy would be strengthened by taking power and bias into account (C. A. Donnelly et al. Nature558, 361–364; 2018). Otherwise, the principles could fall short for issues that involve uncertain facts, disputed values, high stakes and urgent decisions — as in global biodiversity loss and climate change, for example.

Sometimes, complexities in scientific evidence allow several contrasting but equally valid interpretations. In such cases, there is a risk that privileged stakeholders associated with one way of thinking might unduly influence the particular values and interests prioritized in that synthesis.

Scientific aspirations, integrity and practices are crucial for challenging this authority. But if scientific disciplines and organizations deny or become complacent about their own forms of bias, then claims that purport to be definitive and objective could distort decision-making.

Evidence synthesis therefore needs to highlight contrasting valid framings of the best available evidence. A plural and conditional picture that is rigorous in embracing both social and natural sciences is more robust than single, evidence-based prescriptions. Analyses are inevitably influenced by politics. By improving transparency, those who hold power and privilege in and around science become more accountable.

We therefore suggest adding a fifth principle of open-mindedness, with mandates to examine the evidence from outside as well as inside science; to explain how contrasting values and interests yield divergent interpretations and prescriptions; and to evaluate the effects of power and privilege within established practices of evidence synthesis.